In a light source used for illumination of a projector and so on, the light source with a uniform angle intensity distribution is required to perform uniform images.
When an image display apparatus uses a laser beam as the light source, since coherence (coherency) of the laser beam is high, there emerges unevenness of brightness in light intensity (speckle) due to interference.
For example, in a case where beams from a single laser beam divided by an optical element are superimposed with each other, or in a case where the laser beam is scattered by fine unevenness on a surface of an optical element or its internal defect, the above unevenness of brightness emerges on a screen because of mutual interference of the laser beams.
When a laser beam with high coherence is employed, unevenness in light intensity due to speckle becomes large enough to be visually recognizable clearly, resulting in significant deterioration in image quality.
As an improvement measure therefor, there has been developed an image display apparatus equipped with a laser light source apparatus that outputs a light beam having a uniform illuminance distribution.
FIG. 6 is a configuration diagram showing an image display apparatus disclosed in Patent Document 1.
This image display apparatus is equipped with a laser light source apparatus that outputs a light beam with a uniform illuminance distribution; this laser light source apparatus is configured with: a laser light source 101 having a plurality of light emitting points each emitting a laser beam; a condenser lens 102 that converges the laser beams emitted from the plurality of light emitting points in the laser light source 101; and a diffusion element 103 that is arranged near a condensing point of the laser beam by the condenser lens 102 and has a hologram for widening a divergence angle of the laser beam.
The diffusion element 103 of the laser light source apparatus has a diffusion effect that widens the divergence angles of the laser beams in such a manner that two or more laser beams of a plurality of laser beams are overlapped with each other; thus, spatial coherency of the light beams after overlapping of the plurality of laser beams is decreased, so that unevenness in light intensity due to the speckle is reduced.